To give you adequate pointers, we will need to know which type of HMI you plan to program (operator panel, Runtime application on a PC...) and also the software you plan to use to do this.

But first, the basic generalities.

You say you have no PLC programming experience, which does not mean you cannot plan and program the HMI; you must simply be aware that you must ensure the PLC is progrmmed and configured correctly, that all the values you need to show on the HMI screens are available (and correctly scaled) for your application in the PLC program, and that there is an adequate network connection available on the PLC to communicate with the HMI. You just might have to intervene in the PLC program (or have someone help you out) if this needs to be corrected during the project.

So, first, there must be a communication channel between the PLC and the HMI application. In Siemens panels or PC Runtimes, this is done in the HMI configuration: selection of the channel, setup of the connection, selection of the tags (registers in the HMI software that are linked to PLC addresses).

Once this is done, you start designing screens. An HMI screen is a view of either part of the plant you want to control, or of logical controls in the plant. For example, you could show a view of the project piping, with the pumps, tanks, valves, with all necessary instrumentation and values (speed, flow, levels, temperature...) so that the operator can control the process.Or you could show a single machine, with the incoming material, the transformation process and material exit, with conveyor speed, material volume and weight data.

Then you must prepare your alarms and messaging system, so the operator is made aware of any discrepancy in production, and you must organize your screens so the operator can reach any of them as needed, with navigation tools that the floor operators can intuitively follow to diagnose any problem in the process with the data on screen.

For more information, have a look at this sample manual (for Basic Panels, in this case). It will show you the basic steps you can learn to apply generally to any HMI application.